Monocytes are large than lymphocytes. They have much cytoplasm with a bean shpaed necelus. These comprise only 2% to 10% of total leucocytes in the blood. They are phagocytic and formed in lymph nodes and spleen.
WBC which feed on bacteria by engulfing them are called phagocytes. Hey engulf bacteria and broken or dead cells with the help of their pseudopodia; this process is called phagocytes reach that place and feed on them or produce some substance which is harmful for bacteria.
When there is an injury in body then phagocytes press themselves out of the well of the capillaries. This process is called diapedesis. The pahgocytes act as soldiers to flight bacteria and other foreign substances and from thick yellow coloured fluid called pus which contains dead cells etc. the pus come out of the body if however, they fail to destroy bacteria or germs, then the body becomes diseased.
The harmful bacteria and germs are also destroyed by another method. Some blood proteins change into a anew type of protein called antibodies or antitoxins. Leucocytes play a very important role in the formation of this substance. Lucocyte generally remain alive for one to two days. Majority of them are lost in fighting bacteria and other germs.